Pneumatic tube carrier systems are a well-known means for the automated transport of materials between, for example, an origination location and any one of a plurality of destination locations. A typical system includes a number of pneumatic tubes interconnected in a network to transport carriers between user stations. Various blowers and transfer units provide the force and path control means, respectively, for moving the carriers through and from tube-to-tube within the network. Generally, transfer units move or divert pneumatic carries from a first pneumatic tube to a second pneumatic tube in order to route the pneumatic carrier between locations, or stations, in the network.
The pneumatic tubes forming the network of a pneumatic tube system may be arranged in any manner that allows the carriers to be transferred between various stations. Generally, systems include a number of individual stations interconnected to the network by a single pneumatic tube. The single pneumatic tube transfers carriers to and from the station under pressure and vacuum.
Large pneumatic tube systems often require a complex network of interconnected tubes. Further, to provide functionality to separate portions of such large systems, most such systems are divided into multiple zones. Typically, each zone includes a set of stations that receive pneumatic pressure and/or vacuum from a common blower. For instance, a transfer unit that receives pressure and/or vacuum from the common blower may connect to each station of such a zone. This transfer unit permits carriers received from a tube connected to one of the stations to be transferred to a tube connected to another of the stations. However, effective use of the pneumatic tube system requires connecting different zones to permit inter-zone traffic (i.e., transfers from zone to zone). Such inter-zone connections are sometimes made using dedicated unidirectional tubes. In such instances, a zone may interconnect directly to one or more adjacent zones. Accordingly, to effect transfer of a carrier from a sending station to a receiving station may require passing a carrier through more than one zone and/or multiple inter-zone connections.
In order to enhance the functionality of a pneumatic tube system, such systems concurrently process multiple carriers. However, when inter-zone paths of two or more carriers conflict, a gridlock or deadlock condition may occur, which does not permit these carriers to proceed. One solution for alleviating gridlock situations in pneumatic carrier systems is to include at least one bypass pipe to which one carrier may be moved within a particular zone while another transaction passes through the zone. Such bypass typically requires recalling one carrier from an inter-zone connection (e.g., transfer tube) and locating/parking that carrier in a bypass tube to permit a blocked carrier to pass by the parked carrier and enter the now vacated inter-zone transfer tube.